Variable display device and method of driving the same

ABSTRACT

A variable display device includes a display panel; a joint plate installed at a rear surface of the display panel and including a plurality of plates each configured to be rotated by a hinge; and a driving system installed at a rear surface of the joint plate and rotating the plurality of plates with respect to a normal direction to the joint plate, wherein the display panel is variably driven in a flat mode having a flat surface or a curved mode having a curved surface by the joint plate and the driving system.

This application is a continuation of U.S. patent application Ser. No.14/139,034 filed Dec. 23, 2013, which claims priority to Korean PatentApplication No. 10-2013-0116807 filed in Korea on Sep. 30, 2013, both ofwhich are hereby incorporated by reference for all purposes as if fullyset forth herein.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a variable display device, and moreparticularly, to a variable display device and method of driving thesame in a flat mode and a curved mode.

Discussion of the Related Art

With rapid development of information technologies, display devices fordisplaying a large amount of information have been promptly developed.More particularly, various flat panel display (FPD) devices have beenintroduced and spotlighted.

The flat panel display devices include, for example, liquid crystaldisplay (LCD) devices, plasma display panel (PDP) devices, fieldemission display (FED) devices, electroluminescence display (ELD)devices, and organic electroluminescent display (OLED) devices. The flatpanel display devices generally have a thin profile, light weight andlow power consumption and have been rapidly replacing cathode ray tubes(CRT).

Recently, curved display devices have emerged as the next generationdisplay device because the curved display devices enable a user to befurther immersed in watching, to watch realistic images and to feelcomfortable.

In curved display devices, since a distance from the eyes of the user toa center of the screen is equal to a distance from the eyes of the userto sides of the screen, distortion of an image and a decrease inawareness at the sides that the image is blurred at an end viewing angleare minimized. The curved display devices may have advantages such asbetter use of space, the interior and the design and may be used forvarious applications.

Meanwhile, variable display devices having the advantages of the flatpanel display devices with wide viewing angles and the curved displaydevices with increased immersion and comfortableness have been pursuedand researched.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a variable displaydevice and method of driving the same that substantially obviates one ormore of the problems due to limitations and disadvantages of the relatedart.

An advantage of the present invention is to provide a variable displaydevice that is driven in a flat mode and in a curved mode, and a methodof driving the same.

To achieve these and other advantages and in accordance with the purposeof embodiments of the invention, as embodied and broadly described, avariable display device may include a display panel; a joint plateinstalled at a rear surface of the display panel and including aplurality of plates each configured to be rotated by a hinge; and adriving system installed at a rear surface of the joint plate androtating the plurality of plates with respect to a normal direction tothe joint plate, wherein the display panel is variably driven in a flatmode having a flat surface or a curved mode having a curved surface bythe joint plate and the driving system.

In another aspect, a method of driving a variable display device, whichincludes a display panel; a joint plate installed at a rear surface ofthe display panel and including a plurality of plates each configured tobe rotated by a hinge; and a driving system installed at a rear surfaceof the joint plate and rotating the plurality of plates with respect toa normal direction to the joint plate, wherein the display panel isvariably driven in a flat mode having a flat surface or a curved modehaving a curved surface by the joint plate and the driving system,includes first rotating the plurality of plates by the driving systemwith increasing rotational angles as approaching both edge portions ofthe joint plate from a center portion of the joint plate; driving thevariable display device in a curved mode such that the display panel hasa curved surface according to the first rotating the plurality ofplates; second rotating the plurality of plates by the driving systemsuch that the plurality of plates are disposed on a line; and drivingthe variable display device in a flat mode such that the display panelhas a flat surface according to the second rotating the plurality ofplates.

In another aspect, a method of driving a variable display device, whichincludes a display panel; a joint plate installed at a rear surface ofthe display panel; and a driving system installed at a rear surface ofthe joint plate, wherein the driving system includes a motor, aneccentric cam being eccentric with respect to a rotation axis of themotor, a shaft connected to the eccentric cam through a ball bearing, acouple of first levers having first ends fixed to a central area of thejoint plate and second ends, a couple of second levers having third endsconnected to the second ends through a shaft bearing and fourth endsfixed to an edge portion of the joint plate, an angle bearing installedto the shaft, a couple of bearing stoppers disposed at both sides of theangle bearing and fixed to the joint plate, and a shaft fixing blocksupporting an end of the shaft, and wherein a spring is wound around theshaft between the angle bearing and the shaft fixing block, includesrotating the eccentric cam at each of both edge portions of the jointplate by driving the motor; elastically compressing the spring by movingthe shaft and the angle bearing toward a first direction by rotation ofthe eccentric cam; pushing and raising the shaft bearing; raisingconnecting portions of the first and second levers by the shaft bearing;rotating first, second, third, fourth and fifth plates of the jointplate connected to the first and second levers such that the first,second, third, fourth and fifth plates are rotated toward an oppositedirection to the rear surface of the joint plate with increasingrotational angles as approaching edge portions of the joint plate from acenter of the joint plate; driving the variable display device in acurved mode such that the display panel has a curved surface accordingto the joint plate; expanding and restoring the spring by rotating theeccentric cam by the motor, thereby moving the shaft toward a seconddirection opposite to the first direction; lowering the shaft bearing;lowering the connecting portions of the first and second levers by theshaft bearing; rotating the first, second, third, fourth and fifthplates of the joint plate connected to the first and second levers suchthat the first, second, third, fourth and fifth plates are disposed on aline; and driving the variable display device in a flat mode such thatthe display panel has a flat surface according to the joint plate.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention. In the drawings:

FIG. 1A and FIG. 1B are perspective views schematically illustrating avariable display device according to an exemplary embodiment of thepresent invention;

FIG. 2 is a perspective view schematically illustrating a rear side of avariable display device according to an exemplary embodiment of thepresent invention;

FIG. 3 is a perspective view schematically illustrating a backcoversystem according to an exemplary embodiment of the present invention;

FIG. 4A is a perspective view schematically illustrating a joint plateaccording to an exemplary embodiment of the present invention, and FIG.4B is a perspective view schematically illustrating a driving systemaccording to an exemplary embodiment of the present invention;

FIGS. 5A and 5B are perspective views schematically illustrating adriving system installed at a side of a backcover system according to anexemplary embodiment of the present invention, FIG. 5C is across-sectional view of FIG. 5B, and FIG. 5D is a perspective viewschematically illustrating a backcover system in a curved mode accordingto an exemplary embodiment of the present invention; and

FIG. 6 is a perspective view schematically illustrating a motor unit.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Reference will now be made in detail to embodiments of the presentinvention, examples of which are illustrated in the accompanyingdrawings. The same reference numbers may be used throughout the drawingsto refer to the same or like parts.

FIG. 1A and FIG. 1B are perspective views schematically illustrating avariable display device according to an exemplary embodiment of thepresent invention, and FIG. 2 is a perspective view schematicallyillustrating a rear side of a variable display device according to anexemplary embodiment of the present invention.

In FIGS. 1A and 1B and FIG. 2, the variable display device 100 accordingto the exemplary embodiment of the present invention includes a displaypanel 110, an external case 120 and a support 130. The display panel 110displays images, and the external case 120 accommodates the displaypanel 110. The support 130 is connected to a lower part or a rear partof the external case 120 and is fixed to a desk or a surface of a wall.

At this time, a cover glass (not shown) may be disposed at a front sideof the display device 110 to protect the display panel 110.

Here, the display panel 110 may be one of a liquid crystal display (LCD)device, a plasma display panel (PDP) device, a field emission display(FED) device, an electroluminescence display (ELD) device, and anorganic light emitting diode (OLED) device. Beneficially, the displaypanel 110 may be an OLED device, which displays images even when it isbent like a paper.

Since OLED devices are self-luminescent, the OELD devices do not requirea backlight unit and have a thin profile and light weight as comparedwith LCD devices, which are non self-luminescent.

In addition, the OLED devices have better viewing angles and contrastratio than the LCD devices and have merits in power consumption. TheOLED devices are driven by low voltage of direct current (DC), and haverelatively fast response time. Since the OLED devices include solidcomponents, the OLED devices are resistant to outer impacts and arestable under temperatures within a wide range.

Particularly, since a manufacturing process of the OLED devices is verysimple, manufacturing costs of the OLED device are further reduced ascompared with an LCD device.

The display panel 110, which is an OLED device, includes a firstsubstrate and a second substrate facing each other. The first and secondsubstrates are spaced apart from and attached to each other by aprotection layer having an adhesive property.

More particularly, although not shown in the figures, a driving thinfilm transistor is formed in each pixel region on the first substrate,and a first electrode, an organic light-emitting layer and a secondelectrode are sequentially formed on the first substrate. The firstelectrode is formed in each pixel region and connected to the drivingthin film transistor. The organic light-emitting layer emits light. Theorganic light-emitting layer may be formed in each pixel region. Thesecond electrode is formed all over the first substrate and covers theorganic light-emitting layer.

The organic light-emitting layer may emit red, green or blue light andmay be formed by patterning an organic material emitting red, green orblue light in each pixel region. Thus, red, green and blue pixel regionsare sequentially arranged.

The first and second electrodes and the organic light-emitting layerconstitute a light-emitting diode. At this time, the display panel 110may include the first electrode as an anode and the second electrode asa cathode.

The display panel 110 may further include a polarizing unit forpreventing external light from being reflected.

As illustrated in FIG. 1A, when the display panel 110 is driven in aflat mode, the variable display device 100 has relatively wide viewingangles and provides many viewers with news or advertisements from imagesdisplayed by the display panel 110.

Alternatively, as illustrated in FIG. 1B, when the display panel 110 isdriven in a curved mode, the variable display device 100 enables aviewer to be further immersed in watching, to watch realistic images andto feel comfortable.

Namely, since the variable display device 100 is variably driven in theflat mode and in the curved mode, a user can selectively use thevariable display device 100 of the flat mode or curved mode as occasiondemands.

The variable display device 100 is variably driven in the flat mode andin the curved mode by a backcover system 200, which is installed at arear surface of the display panel 110, as illustrated in FIG. 2. Thiswill be described in more detail with reference to accompanyingdrawings.

FIG. 3 is a perspective view schematically illustrating a backcoversystem according to an exemplary embodiment of the present invention.FIG. 4A is a perspective view schematically illustrating a joint plateaccording to an exemplary embodiment of the present invention, and FIG.4B is a perspective view schematically illustrating a driving systemaccording to an exemplary embodiment of the present invention.

In FIG. 3 and FIGS. 4A and 4B, the backcover system 200 includes thejoint plate 210 and the driving system 220. The joint plate 210 contactsthe rear surface of the display panel 110 of FIG. 2 and applies pressureto the display panel 110 such that the display panel 110 switchesbetween the flat mode and the curved mode. The driving system 220 isinstalled to the joint plate 210 and tilts the joint plate 210 at apredetermined angle.

Referring to FIG. 4A, the joint plate 210 has a shape and a sizecorresponding to the display panel 110 of FIG. 2 and includes first,second, third, fourth and fifth plates 210 a, 210 b, 210 c, 210 d and210 e by dividing both edge portions and a central portion and dividingthe central portion into at least three equal parts. The second, thirdand fourth plates 210 b, 210 c and 210 d have the same size, which islarger than that of the first and fifth plates 210 a and 210 e.

Each of the first, second, third, fourth and fifth plates 210 a, 210 b,210 c, 210 d and 210 e is connected to adjacent plate or plates by hingebrackets 213. The hinge brackets 213 each include pins and springsinside and are combined with the plates 210 a, 210 b, 210 c, 210 d and210 e to be rotated as a hinge.

Therefore, the first, second, third, fourth and fifth plates 210 a, 210b, 210 c, 210 d and 210 e are rotated toward the display panel 110 ofFIG. 2 with respect to a normal direction to the third plate 210 c onthe center. At this time, the first, second, third, fourth and fifthplates 210 a, 210 b, 210 c, 210 d and 210 e are rotated with increasingrotational angles as approaching the first and fifth plates 210 a and210 e at both edge portions from the third plate 210 c at the centralportion.

That is, the joint plate 210 has a shape such that the both edgeportions are curved with respect to the normal direction. At this time,since the joint plate 210 includes first, second, third, fourth andfifth plates 210 a, 210 b, 210 c, 210 d and 210 e, a precise curvaturecan be substantially formed.

As illustrated in FIG. 4B, the driving system 220, which is installed toa rear surface of the joint plate 210, includes a motor unit 230, acouple of first levers 241, a couple of second levers 243, and a drivingunit 250. The couple of second levers 243 are connected to the couple offirst levers 241 by a shaft bearing 245, and the driving unit 250 movesconnecting portions of the first and second levers 241 and 243 throughthe shaft bearing 245.

The driving system 220 is installed at each of both sides of the centerof the joint plate 210, that is, the third plate 210 c. Beneficially,more than one driving system 210 may be installed at each side of thethird plate 210 c.

Here, the motor unit 230 includes a motor 231, an eccentric cam 233 anda shaft 237. The motor 231 generates rotatory power, and the eccentriccam 233 eccentrically rotates. The shaft 237 is connected to theeccentric cam 233 through a ball bearing 235 and is disposed movablyforward and backward by rolling motion of the eccentric cam 233.

The motor unit 230 is beneficially disposed at a central area of thejoint plate 210.

First ends of the couple of first levers 241 are fixed to the centralarea of the joint plate 210 in which the motor unit 230 is disposed, andsecond ends of the couple of first levers 241 are connected to thirdends of the couple of second levers 243 through the shaft bearing 245.

Fourth ends of the couple of second levers 243 are connected to the edgeportion of the joint plate 210.

The shaft bearing 245 includes a first roller 245 a and a couple ofsecond rollers 245 b at both sides of the first roller 245 a. Thedriving unit 250 is disposed in the connecting portions of the first andsecond levers 241 and 243 where the shaft bearing 245 is located.

The driving unit 250 includes an angle bearing 251 installed to theshaft 237 of the motor unit 230, a couple of bearing stoppers 253disposed at both sides of the angle bearing 251 and fixed to the jointplate 210, and a shaft fixing block 255 supporting an end of the shaft237. A spring 257 of FIG. 5A is wound around the shaft 237 between theangle bearing 251 and the shaft fixing block 255.

The angle bearing 251 gives pressure to and vertically pushes up thefirst roller 245 a of the shaft bearing 245. The angle bearing 251 hasan inclined surface, which contacts the first roller 245 a and has aslope in a forwarding direction of the shaft 237 with respect to thejoint plate 210.

The couple of bearing stoppers 253 are disposed to correspond to thecouple of second rollers 245 b. The couple of bearing stoppers 253 givepressure to and vertically push up the couple of second rollers 245 b.

At this time, the couple of bearing stoppers 253 have curved surfaces,which face the inclined surface of the angle bearing 251, and the secondrollers 245 b roll and vertically rise along the curved surfaces of thebearing stoppers 253.

As mentioned above, the variable display device 100 of FIG. 2 of thepresent invention is selectively, variably used as the flat mode and thecurved mode by the backcover system 200 installed to the rear surface ofthe display panel 110 of FIG. 2.

Here, a variable process of the variable display device 100 of FIG. 2from the flat mode to the curved mode by the backcover system 200 willbe described in more detail.

FIGS. 5A to 5D are views schematically illustrating a variable displaydevice according to an exemplary embodiment of the present inventionwhen it is varied from a flat mode to a curved mode. For convenience ofexplanation, the driving system will be described in detail.

FIGS. 5A and 5B are perspective views schematically illustrating adriving system installed at a side of a backcover system according to anexemplary embodiment of the present invention, FIG. 5C is across-sectional view of FIG. 5B, and FIG. 5D is a perspective viewschematically illustrating a backcover system in a curved mode accordingto an exemplary embodiment of the present invention.

In FIG. 5A, the motor unit 230 is fixed to the third plate 210 c of thejoint plate 210. The first ends of the couple of first levers 241 arefixed to the third plate 210 c in which the motor unit 230 is disposed,and the second ends of the couple of first levers 241 are connected tothe third ends of the couple of second levers 243 through the shaftbearing 245. The fourth ends of the couple of second levers 243 arefixed to the first plate 210 a.

At this time, the connecting portions of the first and second levers 241and 243 are disposed at a central area of the second plate 210 b, andthe driving unit 250 is disposed at the central area of the second plate210 b.

Here, when the motor 231 of the motor unit 230 is driven, the eccentriccam 233 rotates halfway in one direction, and the shaft 237 moves towarda direction opposite the motor 231, that is, the +Y axis defined in thefigures, by rolling contact of the ball bearing 235 due to the rotationof the eccentric cam 233.

The spring 257 wound around the shaft 237 between the angle bearing 251and the shaft fixing block 255 is elastically compressed by movement ofthe shaft 237 to the +Y axis.

Then, in FIG. 5B, the first roller 245 a of the shaft bearing 245 ispressed by the inclined surface of the angle bearing 251 and pushed andraised toward a vertical direction, that is, the +Z axis defined in thefigures, and at the same time, the second rollers 245 b of the shaftbearing 245 are pushed and raised toward the +Z axis along the curvedsurfaces of the couple of bearing stoppers 253.

Accordingly, the whole shaft bearing 245 is pushed and raised toward the+Z axis, and the first and third ends of the first and second levers 241and 243, which are connected to each other through the shaft bearing245, are also lifted toward the +Z axis.

Since the first and third ends of the first and second levers 241 and243 are lifted, the first plate 210 to which the fourth ends of thesecond levers 243 are fixed is raised together, and as illustrated inFIG. 5C, the first plate 210 a is bent toward the −Z axis and is rotatedwith a predetermined angle by the hinge brackets 213 of FIG. 4A betweenthe first plate 210 a and the second plate 210 b.

At this time, the first plate 210 a is more pressured by the secondlevers 243 and is rotated more than the second plate 210 b. The first,second and third plates 210 a, 210 b and 210 c have a curved shape.

A driving system installed to the other side of the backcover system 200is driven by the same way as described above, and as illustrated in FIG.5D, the backcover system 200 is curved as a whole with respect to thenormal direction.

In the present invention, the backcover system 200 installed to the rearsurface of the display panel 110 of FIG. 2 is rotated as a whole withrespect to the normal direction such that rotating angles increase asapproaching from the central portion to the both edge portions. Thus,the display panel 110 of FIG. 2 is driven in the curved mode where thedisplay panel 110 of FIG. 2 has a curved surface with respect to thenormal direction by the backcover system 200.

On the other hand, when the variable display device 100 of FIG. 2 isvaried from the curved mode to the flat mode, the motor 231 of the motorunit 230 is driven, and the eccentric cam 233 rotates halfway in the onedirection. Then, the spring 257 elastically compressed between the anglebearing 251 and the shaft fixing block 255 is expanded and restored, andthe shaft 237 moves toward a direction facing the motor 231, that is,the −Y axis defined in the figures.

With the movement of the shaft 237 toward the −Y axis, the angle bearing251 also moves toward the −Y axis. The shaft bearing 245, which waspressed by the inclined surface of the angle bearing 251 and the curvedsurfaces of the bearing stoppers 253 and pushed and raised toward the +Zaxis, is lowered.

Accordingly, the first and second levers 241 and 243 are lowered, andthe first plate 210 a, which was bent toward the −Z axis and rotated toform the curved surface, return to its original position. The first,second and third plates 210 a, 210 b and 210 c are disposed parallel ina line, and the variable display device 100 of FIG. 2 is driven in theflat mode.

As disclosed above, the variable display device 100 of FIG. 2 isselectively, variably driven in the flat mode or in the curved mode bythe backcover system 200, which is installed at the rear surface of thedisplay panel 110 of FIG. 2.

Namely, in an open space such as an outdoor or indoor square such asairports or terminals, the variable display device of the presentinvention is driven in the flat mode such that the variable displaydevice has wide viewing angles and news or advertisements from imagesdisplayed by the display panel are provided to many viewers.Alternatively, the variable display device of the present invention isdriven in the curved mode such that the viewer is further immersed inwatching, watches more realistic images and feels comfortable.

Accordingly, the user can selectively use the variable display device100 of FIG. 2 as the flat mode or the curved mode as occasion demands.

In the meantime, the motor 231 of the motor unit 230 may include an ACmotor, and the motor 231 may be installed such that the eccentric cam233 is eccentric with respect to its rotation axis.

Therefore, the variable display device 100 of FIG. 2 is variable betweenthe flat mode and the curved mode due to the halfway rotation of themotor 231.

At this time, when the variable display device 100 of FIG. 2 is variablebetween the flat mode and the curved mode, vibrations or noises mayhardly occur.

That is, as illustrated in FIG. 6, the eccentric cam 233 is installedeccentrically to the rotation axis 232 of the motor 231, and a switchcam 234 is installed onto the eccentric cam 233. The switch cam 234includes first and second switch grooves 234 a and 234 b to control offof the motor 231.

In addition, first and second motor switches 238 a and 238 b areinstalled at both sides of the switch cam 234. The first and secondmotor switches 238 a and 238 b have switches 238 c corresponding to thefirst and second switch grooves 234 a and 234 b.

The first and second switch grooves 234 a and 234 b face each other, andthe switch cam 234 rotates with the eccentric cam 233 by the rotation ofthe motor 231. When the eccentric cam 233 and the switch cam 234 rotatehalfway, the first switch groove 234 b of the switch cam 234, whichcontacted the switch 238 c of the first motor switch 238 a, contacts theswitch 238 c of the second motor switch 238 b.

At this time, off signals from the motor switches 238 a and 238 b areprovided to the motor 231, and the motor 231 stops rotating.

In the variable display device 100 of FIG. 2 of the present invention,since the motor 231 and the eccentric cam 233 rotate halfway, thevibrations and noises due to the rotation of the motor 231 and theeccentric cam 233 hardly occur.

As mentioned above, the variable display device 100 of FIG. 2 isselectively, variably driven in the flat mode or in the curved mode bythe backcover system 200, which is installed at the rear surface of thedisplay panel 110 of FIG. 2.

Accordingly, in an open space such as an outdoor or indoor square suchas airports or terminals, the variable display device of the presentinvention is driven in the flat mode such that the variable displaydevice has wide viewing angles and news or advertisements from imagesdisplayed by the display panel are provided to many viewers.Alternatively, the variable display device of the present invention isdriven in the curved mode such that the viewer is further immersed inwatching, watches more realistic images and feels comfortable. Thevariable display device of the present invention can be selectively usedfor the convenience of the user.

It will be apparent to those skilled in the art that variousmodifications and variation can be made in the present invention withoutdeparting from the spirit or scope of the invention. Thus, it isintended that the present invention cover the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A variable display device, comprising: a displaypanel configured to be variably driven in a flat mode having a flatsurface or a curved mode having a curved surface; a joint plateinstalled at a rear surface of the display panel and including a centerplate between a plurality of plates including first, second, fourth andfifth plates each configured to be rotated by a hinge; and a pair ofdriving systems installed at a rear surface of the joint plate, facingagainst each other and rotating the plurality of plates with respect toa normal direction to the joint plate, each driving system including amotor unit on the joint plate and a driving unit on an immediatelyadjacent plate, wherein the motor unit includes a motor, an eccentriccam being eccentric with respect to a rotation axis of the motor, and ashaft connected to the eccentric cam, and wherein the motoreccentrically rotates the eccentric cam in less than a full revolution,which moves the shaft in a linear direction substantially parallel withthe rotation axis of the motor, depending on a rotational direction ofthe eccentric cam, wherein the joint plate further includes a thirdplate, and wherein each of the first, second, third, fourth and fifthplates is connected to an adjacent plate by a hinge bracket.
 2. Thedevice according to claim 1, wherein the shaft is connected to theeccentric cam through a ball bearing.
 3. The device according to claim2, wherein a switch cam is installed onto the eccentric cam having firstand second switch grooves, and first and second motor switches havingswitches corresponding to the first and second switch grooves areinstalled at both sides of the switch cam.
 4. The device according toclaim 3, wherein the eccentric cam rotates halfway.
 5. The deviceaccording to claim 1, wherein the driving unit includes an angle bearinginstalled to a shaft, a couple of bearing stoppers disposed at bothsides of the angle bearing and fixed to the joint plate, and a shaftfixing block supporting an end of the shaft, and wherein a spring iswound around the shaft between the angle bearing and the shaft fixingblock.
 6. The device according to claim 5, wherein the shaft bearingincludes a first roller and a couple of second rollers at both sides ofthe first roller, and wherein the angle bearing has an inclined surfacecontacting the first roller, and the couple of bearing stoppers havecurved surfaces facing the inclined surface and contacting the secondrollers.